close #304

app/controllers/admin/communication/extranets_controller.rb

app/models/communication/extranet.rb

app/models/concerns/with_abouts.rb

app/views/admin/communication/_abouts.html.erb

app/views/admin/communication/extranets/_form.html.erb

app/views/admin/communication/extranets/index.html.erb

app/views/admin/communication/extranets/show.html.erb

app/views/admin/communication/websites/_form.html.erb

config/locales/communication/en.yml

config/locales/communication/fr.yml

...te/20220411133002_add_about_to_communication_extranets.rb

db/schema.rb

test/fixtures/communication/extranets.yml

test/models/communication/extranet_test.rb